[Cone-beam CT analysis on the treatment efficacy in the vertically impacted maxillary central incisors]

Objective: To analyze the treatment efficacy in the vertically impacted maxillary central incisors using cone-beam CT (CBCT) and explore the treatment timing and the influence of orthodontic traction on the root development and alveolar bone height in the mixed dentition. Methods: Twenty-two patients with vertically impacted maxillary central incisor who were admitted to the Department of Orthodontics, Stomatological Hospital affiliated to Nanjing Medical University from December 2012 to December 2017 were selected [12 males and 10 females, (9.2±0.9) years]. Based on the dental age, patients were classified as early treatment group (teeth ranging from a third to two thirds of root formation, n=12) and late treatment group (teeth with nearly or fully complete root formation, n=10). The contralateral maxillary central incisor was used as the control. Three-dimensional reconstruction of CBCT before treatment, after treatment and one year after treatment was carried out to measure root length, tooth surface area, tooth volume, labial and lingual apical alveolar bone thickness, the loss of labial alveolar bone height and intraosseous root ratio. The clinical crown length was measured in the mouth. The difference values of the measurement variables between the impacted teeth and the control teeth were calculated and analyzed(measurement values of impacted teeth were subtracted from control values). Results: The values of root length difference beween the impacted teeth and the control teeth in the early and late treatment group were (1.58±1.56) mm and (2.57±1.00) mm, respectively after the treatment and the values were significantly less than those corresponding values before treatment [(3.47±1.40) and (3.36±0.79) mm] (P<0.05). After the treatment, the values of the surface area and volume difference between the impacted teeth and the control teeth in the early treatment group [(0±34) mm(2) and (-10±44) mm(3)] were significantly less than those corresponding values before treatment [(38±31) mm(2) and (55±70) mm(3)] (P<0.05). The value differences of any measurement variables between the early and late treatment group were not significantly different after the treatment (P>0.05). The root length and intraosseous root ratio of the impacted teeth after the treatment in the early and late treatment group were significantly less than those of the control teeth after the treatment (P<0.05). The clinical crown length, the loss of labial alveolar bone height of the impacted teeth after the treatment were significantly larger than those of the control teeth after the treatment (P<0.05). Conclusions: Orthodontic traction promoted the root growth and development of the vertically impacted maxillary central incisors. However, the root length and alveolar bone height still cannot reach the normal level after treatment. Treatment timing had no effect on root development and alveolar bone height of vertically impacted maxillary central incisors in mixed dentition.